1. Field of the Invention
The present invention relates to a thin-film magnetic head with a tunnel magnetoresistive effect (TMR) element.
2. Description of the Related Art
It has been demanded to enhance reading performance of a thin-film magnetic head with increase in a disk recording density of a hard disk drive (HDD). To satisfy such demand of enhancement in the reading performance, widely used is a magnetoresistive effect (MR) head provided with an MR read head element or a giant magnetoresistive effect (GMR) head with a GMR read head element.
In fabricating such MR head or GMR head, since the dimension of the head element namely the MR or GMR element is small whereas the dimension of electrode terminals electrically connected to the MR or GMR element is large, electrostatic discharge may occur to pass electrical charges through the MR or GMR element causing the element to deteriorate or damage.
To prevent such electrostatic damage of the head element, Japanese patent publication No. 10233011A discloses a magnetic head provided with a resistor element of 500Ω to 10 kΩ connected between lead conductors or electrode terminals of an MR element or GMR element for feeding the electrostatic charges there through.
Recently, a TMR head with a TMR element, which can deliver two or more times the MR ratio of the GMR head is aggressively developed. The TMR head has a fundamentally different structure from that of the MR head and the GMR head. For example, in the TMR element, there is an insulation barrier layer and the sense current flows in a direction perpendicular to planes of laminated layers. Thus, the TMR head has considerably different characteristics from that of the MR head and the GMR head. For example, although the MR head and the GMR head have element resistances of about 10–50Ω, the TMR head has a higher element resistance than them by an order of magnitude.
In order to achieve higher recording density, recent magnetic heads are required to have a narrower track width and a lower height causing the element resistance of the TMR element to more increase. With the increase in the element resistance of the TMR element, the cutoff frequency thereof decreases and therefore it is difficult to comply with the high recording density.
It is known that a withstand voltage of the TMR element with the current size (element width and element height) is lower than that of the GMR element with the same size. Therefore, if the element size of the TMR element reduces, not only breakdown of the element may easily occur but also its applicable margin will be lowered due to the reduced current capacity that is caused by increase in the element resistance and by decrease in the breakdown voltage. Furthermore, in case that the element size of the TMR element reduces, resistance variation between the TMR elements will be easily induced even if they are fabricated under the same precision. This variation in element resistance becomes a serious problem in the manufacturing of a TMR head.
For such TMR head, it is impossible to prevent electro-static destruction (ESD) with reliability even if a resistor element with a resistance value of 0.5–10 kΩ is connected in parallel with the TMR element as described in Japanese patent publication No. 10233011A, or a resistor element with a higher resistance value of 5–100 kΩ is connected in parallel with the TMR element. Also, if the resistor element connected in parallel with the TMR element has a high resistance value as described in Japanese patent publication No. 10233011A, an apparent resistance value of the TMR head that is a combined resistance value RTOTAL of a resistance value of the TMR element and a resistance value of the connected resistor element becomes high causing the cutoff frequency of the TMR head to prevent from increasing.